The present disclosure relates generally to electron microscopes and more particularly to an electron microscope using radio frequencies and/or super-cooling.
It is known to employ transmission electron microscopes and scanning electron microscopes to obtain a magnified image of a specimen. Exemplary conventional electron microscopes are disclosed in U.S. Pat. No. 5,811,804 entitled “Electron microscope with Raman Spectroscopy” which issued to Van Blitterswijk et al. on Sep. 22, 1998. This patent is incorporated by reference herein. Another approach is disclosed in U.S. Pat. No. 7,154,091 entitled “Method and System for Ultrafast Photoelectron Microscope” which issued to Zewail et al. on Dec. 26, 2006, and is incorporated by reference herein. Such a device, however, employs a high repetition rate and only emits approximately one electron per each 10 nanosecond shot; even if the specimen event only lasts for 10 nanoseconds then a poor quality image will likely be created if the event is not precisely reproducible.
In many traditional electron microscopes for time-resolved studies, the imaging is carried out in pulse mode, which must compress electrons in a continuous transmission electron microscopic stream into short packets. In a sub-nanosecond arrangement, the density of electrons in packets reaches some 7-9 orders of magnitude higher than that in a steady stream. Such an implementation proves to be detrimental for traditional electron optics used in electron microscopes. Moreover, because of the strong coulombic dispersive forces and statistical fluctuations associated with the high-density electron packets, the coherence, spatial focusing, and ultimately the time resolution needed for freeze-frame imaging of atoms, are destroyed. This well-known space-charge problem has so far hindered any significant progress in using a high-density beam in a conventional microscope to form an atomically sharp image in a sub-nanosecond time scale.
Furthermore, experiments have been made with a dynamic transmission electron microscope. Such a device is disclosed in LaGrange, T. et al., “Single-Shot Dynamic Transmission Electron Microscopy,” Appl. Phys. Lett. 89, 044105 (2006). While this device provides a large quantity of electrons, it does so in a very slow 1 nanosecond pulse. Therefore, it is not fast enough to provide a clear freeze-framing image before the sample or reaction changes. Generally, to produce a clear image in time-resolved microscope, its time resolution must be better than the atomic reaction time scale, typically on 1 picosecond or less timescale.
In accordance with the present invention, an electron microscope is provided. In another aspect, an electron microscope employs a radio frequency which acts upon electrons used to assist in imaging a specimen. Furthermore, another aspect provides an electron beam microscope with a time resolution of less than 1 picosecond with more than 105 electrons in a single shot or image group. Yet another aspect employs a super-cooled component in an electron microscope. Moreover, a further aspect of an electron microscope uses a radio frequency wave to assist in bunching or increasing the density of a series of electrons. A method of operating an electron microscope is also set forth.
The electron microscope of the present invention is advantageous over traditional devices. For example, space-charge effects in a short-pulse electron beam are overcome by use of a radio frequency electron pulse compressor or cavity in an electron microscope beam column with a high-field photo gun, in one aspect. This serves to advantageously achieve much higher intensity images and time resolution than conventional time-resolved microscopes. Furthermore in an aspect, the present electron microscope is advantageously more flexible in terms of pulsed mode imaging, such that a probe size can be easily tuned from nanometer to micrometer, and it can be easily switched from a diffraction mode to a microscopy mode. Additionally, the present electron microscope allows for retrofitting radio frequency cavities onto previously assembled electron microscopes thereby significantly enhancing time-resolution but at less than half the cost of an entirely new microscope. Additional advantages and features can be found in the following description and appended figures.